1. Field of the Invention
This invention relates to a method to recover metals and more specifically this invention relates to a method for recovering and purifying transition metals from contaminants.
2. Background of the Invention
The daughter product of 99Mo is 99mTc. 99mTc is the most commonly used radioisotope for nuclear medicine. It is used in approximately two-thirds of all nuclear medicine imaging procedures.
Most of the world's supply of 99Mo is produced by fissioning 235U in high-enriched (generally 93 percent 235U) uranium targets.
An alternative means to produce 99Mo is using Mo targets. 99Mo can be produced in a reactor by the 98Mo (n, gamma) 99Mo reaction on a natural Mo target or an enriched 98Mo target, or by an accelerator using the 100Mo (gamma, n)99Mo reaction on an enriched 100Mo target. 99mTc− also can be produced directly using 100Mo(p,2n)99mTc. Enriched Mo material (100Mo or 98Mo) is produced from enriching natural Mo and is very expensive. As such, the material needs to be recycled.
One of the ways to separate 99mTc from Mo is using commercially available technetium Tc-99m generators such as RADIOGENIX (Na99mTcO4) from NorthStar, (Madison, Wis.). RADIOGENIX provides Sodium Pertechnetate Tc-99m injection. Sodium Pertechnetate Tc-99m is an inorganic compound with the formula Na99mTcO4. This requires a solution of potassium molybdate (K2MoO4) in approximately 5 moles/liter (M) potassium hydroxide (KOH). Once the 99Mo is decayed, Mo needs to be recovered from this solution that contains approximately 1.8 kg of potassium (K) per kg of Mo. Keeping in mind that the starting concentration of potassium in the enriched material (100Mo,,98Mo) feedstock is below 100 mg/kg of Mo, and that any recovered Mo must be at least that pure, the aforementioned NorthStar protocol introduces large quantities of potassium that must be removed.
A major supplier of 99Mo is Nordion, Inc., (Ottawa, Canada) providing 40 percent of the world's supply. However, the Chalk River Laboratories (Deep River, Ontario, Canada) NRU reactor, which produces 99Mo for Nordion plans to cease production in 2016. There is no U.S. producer of 99Mo.
A need exists in the art for a process for harvesting and purifying transition metals such as Mo, Tc, Ti, Ga, Sb, Zn, Sn, and Nb. The process should not generate large volumes of secondary waste streams as is now the case with state of the art protocols. The process should have the ability to process large quantities of transition metals in a minimal number of steps (i.e., one or two extraction steps). Lastly, the process should employ a continuous protocol, including recycling of organic extraction liquors, and counter-current solvent extraction techniques.